A new study in Science says 20 percent of terrestrial and marine vertebrates …

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Twenty years ago, nearly all the world’s nations agreed to significantly reduce the loss of biodiversity by 2010. (The United States signed the accord but, like other treaties, the Senate has not ratified it.) Well, it’s 2010 and we are nowhere near that goal. While the Convention on Biological Diversity is currently meeting to update its targets for 2020, a new study released by Science says one-fifth of the world’s vertebrate species are threatened with extinction. But the good news is things would be a whole lot worse if we had done nothing at all.

"What our results show is that conservation efforts are not wasted. They are making a noticeable difference," said Ana Rodrigues, a researcher at the Center for Evolutionary and Functional Ecology in Montpelier, France, and one of the authors of the study. The researchers compiled the status of over 25,000 vertebrate species as rated by the International Union for the Conservation of Nature’s Red List. "The rates of decline in the Red List index would have been 18 percent steeper" in the absence of conservation programs.

Preserving biodiversity may seem like a frivolous goal to some, given the current economic recession, but diverse and stable ecosystems provide many services, including clean drinking water, pollination, pest control, pollution abatement, and so on.

"These ecosystem services, as they are called, are estimated to be worth $33 trillion per year, ten times the size of the UK GDP, for example," said Stuart Butchart, an ornithologist with BirdLife International and one of the paper’s authors. "Economists have calculated that not stepping up our efforts on biodiversity loss will cost us seven percent of the global GDP by 2050, and that doesn’t even include the consequences of resource conflicts, refugees, and political instability that will happen when these systems reach tipping points of collapse."

Regardless of the economic costs of lost biodiversity, the study’s raw numbers are disheartening. One in eight birds are threatened with extinction, along with one in four mammals, one in seven bony fish, one in four reptiles, one in three amphibians, and one in three sharks. While the survey found threatened vertebrates on land and in oceans across the globe, most of the imperiled species inhabit tropical regions.

Southeast Asia stands out above other regions as having both the highest concentration of threatened species and the highest rate at which species decline in status. What’s to blame? "It’s a combination of habitat loss and overexploitation," Rodrigues told Ars. Oil palm plantations have gobbled up large swaths of forest in the region, while the bushmeat and cage-bird trades threaten many species in the forests that remain, Butchart added.

In other regions, invasive species and new diseases have been largely responsible for dwindling populations and outright extinctions. Chytridiomycosis, an infectious disease, has been pummeling amphibian populations in California, Central America, Australia, and the Andes Mountains. In fact, the disease has so widely affected amphibian populations that more than 40 percent of amphibian species are classified as threatened on the Red List.

Though a lower percentage of birds and mammals are threatened, many are under constant pressure from invasive species. Species introduced to the Hawaiian Islands have driven many native fauna extinct and many more to the brink, Butchart said. Fortunately, conservationists have become relatively adept at dealing with invasive species, at least compared to other threats like habitat loss. Forty percent of animals threatened by invasive species improve in status once the interlopers are dealt with, the study reports.

There have also been a few remarkable recoveries. The Mauritius kestrel, of which there were only four in 1974, is nearly fully recovered with around 1,000 birds thanks to a successful captive breeding program. The humpback whale is another standout example. Due to the 1955 ban on commercial whaling, one of the world’s largest mammals is now classified as “least concern.”

Conservation’s successes prove extinction threats are not entirely intractable, though many problems like habitat loss will require political, social, and economic cooperation to successfully tackle. More protected areas, both on land and in the ocean, will go a long way, but there is not one answer. "What we need is tailored solution to a particular problem," Rodrigues said. "It’s not just one solution that will work everywhere in the same way."